Catheters have found widespread use in medical procedures, such as percutaneous transluminal coronary angioplasty (PTCA) or for delivery of stents. A typical endoluminal deployment system includes an inner catheter or cannula, which may also be arranged as a pusher and/or dilator (hereinafter referred to as an inner catheter) and a sheath covering the inner catheter. An implant or prosthesis is carried on the inner catheter and is fixed thereto by means of the covering sheath, with or without one or more restraining wires or any of a number of other known retention systems.
The implant or prosthesis might be a stent, a stent graft, a filter, an occlusion device or any other implantable device of such a nature.
Most catheters are guided to the application site by sliding the catheter along a guide wire, which has been carefully advanced and arranged within the patient. During advancement of the catheter along the guide wire, it is important to keep the guide wire steady. Ordinary catheters are guided to the application site in a patient by sliding the catheter along a guide wire extending all the way through a lumen of the catheter from the proximal end to the distal end thereof. To enable the physician to hold or manipulate the guide wire during advancement of the catheter along the guide wire, it is necessary to have an excess length of guide wire. The guide wire must hence have a length of about twice the length of the catheter, e.g. 3 m in total, which greatly impedes the procedure. An important sub-category of catheters are catheters of the so-called rapid exchange type, which greatly facilitate operation, especially exchange of catheters if it is found during a procedure that a different kind or size of catheter is needed for the specific purpose. In the rapid exchange catheter, the guide wire only passes through a minor part of the catheter at the distal end thereof, whereas along a majority of the catheter, the guide wire runs in parallel with the catheter. Hence it is not necessary to have an excess length of guide wire.
Once the distal end of the inner catheter has been positioned inside a patient, typically at the site of the patient's vasculature to be treated, the device is released and deployed in the desired position. The deployment operation involves retracting the covering sheath so as to expose the device to be implanted, which device is then deployed, either by self-expansion or by means of an expansion device such as an inflatable balloon located internally of the device. In the case where the device is also held by restraining wires, these are withdrawn, typically after retraction of the sheath. Restraining wires may or may not be used in such apparatus, generally depending upon the nature of the device to be deployed, size restrictions and the particular medical application or intervention procedure.
An important feature of catheters is the transmission of force, the so-called push force, from the proximal end to the distal end of the catheter. This transmission significantly affects the physician's ability to direct the distal end of the catheter into a body lumen of a patient by manipulating the proximal end thereof. Another important feature of catheters is the flexibility of the distal end to bend and conform to the body lumen wall without causing any injury to the lumen wall. Hence catheters, especially of the rapid exchange type, are commonly manufactured of a metal proximal shaft portion of relatively stiffness, and a relatively flexible plastics distal portion bonded to the metal shaft portion. An abrupt change of properties between the shaft portion and the distal portion however increases the risk of twist and kinking. Hence there is a need to provide a good transition between the relatively stiff proximal section to the relatively more flexible distal section to provide a sufficient resistance to twist and kinking while maintaining flexibility and ability to bend.
A problem with this type of arrangement is that kinking can occur at the transition between the portions having different flexibilities. This kinking can result in closure of the lumen of the catheter. In order to control the flexibility, some inner catheters are provided with a wire fixed to the internal surface of the inner catheter at the point where the two parts having differing flexibility are connected. This is illustrated in FIG. 1. However, whilst the wire provides a stiffening function, it results in an uneven distribution of flexibilities in the radial direction of the inner catheter.
Other examples of stiffening members are disclosed in U.S. Pat. No. 5,658,251, U.S. Pat. No. 6,066,114 and U.S. Pat. No. 6,746,423.
US 2007/0010786 discloses a catheter suitable for advancement through a body passageway of a patient. The catheter comprises a catheter body which is flexible to provide the necessary trackability for the catheter to advance through a body passageway, and two stainless steel reinforcement wires extending along the catheter body which provide the necessary pushability to advance the catheter through the passageway. The reinforcements are positioned diametrically opposed to one another by approximately 180 degrees on opposite sides of the longitudinal axis of the catheter, and the catheter body is relatively soft and twistable. This configuration enables the entire catheter to twist spontaneously during advancement so that the reinforcements orientate themselves along a plane of neutral bending during advancement of the catheter.
Kinking between portions of differing flexibility is particularly problematic for a rapid exchange balloon catheter.